The present patent application claims foreign priority benefits under 35 U.S.C. xc2xa7119 to Italian patent application No. SV2000A000027, filed Jun. 22, 2000, now pending.
The invention relates to a method of ultrasound imaging, including the following steps:
transmitting ultrasonic beams generated by transducers into an object volume corresponding to an object body or a part thereof;
receiving and storing echo signals generated by the ultrasonic beams in said object volume;
processing the received signals into image data associated to image dots or lines of a video display;
displaying at least a few image data on the display in accordance with parameters set by the user and related to a predetermined section or projection plane of the image of said object volume;
processing of ultrasonic beams and/or displaying being specifically predetermined with reference to a preliminary selection of a section plane or an image projection plane of the object volume to be imaged.
Methods of this type are known, for instance, from U.S. Pat. No. 5,396,890 or EP 952,463 or U.S. Pat. No. 5,226,113, U.S. Pat. No. 5,928,151 and U.S. Pat. No. 5,497,776.
These known methods aim at performing three-dimensional ultrasound imaging by a number of different techniques, e.g. acquiring a succession of section planes of the object body, processing the individual reflected echoes in each plane and constructing a three-dimensional image memory in which the received echo signals are associated to a set of voxels, i.e. image dots of a three-dimensional image, while accounting for the relative position of the individual scan planes.
During image acquisition, the whole object volume is generally scanned, through successive two-dimensional section planes staggered to a predetermined extent to cover the whole object volume. Then, the signals of the reflected echoes are processed and transformed into image data in the form of a three-dimensional matrix of image dots. This process must be substantially exhaustive to allow the desired image to be displayed in a plane having any spatial orientation and crossing the object volume. Hence, a selected image may be displayed only after scanning the whole volume and, above all, after completely processing the echo signals to generate the three-dimensional image data matrices. Therefore, image displaying times are relatively long and require highly powerful and costly hardware to obtain an acceptable processing time. Moreover, these very long displaying times are a severe shortcoming when related to the difficulties the patient encounters in keeping perfectly still for long periods of time and when transient events are to be observed whose starting time is not exactly predefined. An important example consists in the combined use of ultrasound imaging with the so-called contrast agents. These substances are injected into the tissues under examination. A certain time, of a few tens of seconds, passes before they reach the object region. Further, the time during which contrast agents remain in the object tissues, as regards both their passage therethrough and their decay, is short, also being of the order of a few tens of seconds. Hence, by using prior art imaging methods, it may be frequent that scanning is performed when contrast agents have not reached the object region yet. If this is the case, the doctor or the user will only be able to assess this condition later, when processing is completed, hence in unfavorable conditions, and will not have the time for a new image acquisition in order that imaging may take place when contrast agents are present or have not decayed in the object region. In this case, a new injection of contrast agents will be required to repeat scanning. Such a situation is definitely undesirable, as it reduces the non-invasiveness degree of the ultrasound imaging method.
Identical or similar problems are encountered when the probe is not properly positioned, whereby even though scanning is performed while contrast agents are present in the object region, it must be repeated, for instance if probe orientation does not allow scanning of the volume of interest and provides an unusable or anyway useless image.
The multiple techniques described in the above documents are based on a concept shared by all ultrasound imaging methods or systems, i.e. that the user may first select an imaging type, related to an imaging mode, e.g. the so-called B-mode, Doppler, Power Doppler, harmonic imaging, etc.
The selection of the view or section plane of interest takes place after image acquisition and processing of image data matrices. These steps are substantially preset in the apparatus.
The invention has the object of providing an ultrasound imaging method, particularly in three dimensions, which allows to obviate the drawbacks of prior art methods, without requiring any considerable complication of the method and higher costs of the apparatus for implementing it, while allowing a real time image display in section or projection planes having any orientation in space and with reference to the volume of interest.
The invention achieves the above purposes by providing a method of ultrasound imaging as described above, which has the following additional steps:
defining a virtual volume coincident with the object body or part thereof or a three-dimensional reference system, provided it has a definite orientation with respect to the imaging planes generated by the ultrasound probe;
selecting the section plane of the object body and/or part thereof along which ultrasound imaging is to be performed.
determining the position-defining coordinates for the dots which form said section plane along which imaging is to be performed, with reference to the virtual volume;
restricting the scanning operation to the region which coincides with said section plane along which imaging is to be performed;
transmitting the transmission signals and receiving the reflected echoes only along such lines of view of the probe which coincide with the surface or the projection slice of the selected section plane along which imaging is to be performed;
only processing and displaying the received echo signals.
This method drastically reduces the number of steps required for image data processing from the received signals and considerably speeds up such processing. In fact, thanks to the preliminary selection of the section plane of the object body or part thereof to be imaged, the method restricts not only the amount of signals to be processed for imaging, but also scanning times, with the probe transmitting and receiving not along the whole scan plane thereof, but only for a limited slice, coinciding with said projection region of the selected section plane, along which imaging is to be performed.
It will be understood that the principle of this method is reversed as compared to the one currently in use. At present, as stated above, the modes of transmitting and receiving ultrasonic signals and processing reflected echoes are preset and independent from the section plane or projection plane of the object volume to be imaged and the selection of said planes, or more particularly of their orientation with respect to the object volume takes place a posteriori, i.e. when substantially all useful signals have been converted to image data by scan converters. In the present invention, it is the selection of the section plane or of the projection plane to be imaged which determines the modes of transmitting and receiving ultrasonic signals, as well as processing modes, aimed at generating the image data three-dimensional matrix, wherefrom images are generated. From said transmission and reception, i.e. from the scanning operation, all the regions which do not intersect or fall within the selected section plane along which imaging is to be performed, are excluded, to filter out all the signal portions which do not contribute to form dots, lines or unit volumes of the image coinciding with or belonging to the section plane to be imaged.
It is important to observe that the principle of the method of the invention may apply to any type of ultrasound imaging, for instance B-Mode, Doppler, Power Doppler, Harmonic Imaging, and even to combinations of said modes.
The above principle also applies to all types of probes.
Particularly, said principle is suitable for a real time display of so-called three-dimensional ultrasound images.
According to an improvement, it is possible to receive and store reflected echo signals even of regions which are not coincident with the selected section plane or with the selected projection plane to be imaged and to provide, simultaneously to or after image processing of signals coinciding with said planes, even processing of the remaining signals or signal portions into image data.
As a further improvement, there may be provided several modes of transmitting and receiving ultrasonic signals along the different scan lines which form each scan plane of the probe, depending on their being coincident with the section plane to be imaged or not coincident therewith. In fact, it is possible to perform scanning with non optimal parameters, hence in a shorter time, for the scan lines which do not coincide with the section plane along which imaging is to be performed, whereas parameters are optimized for the lines which coincide with the section plane along which imaging is to be performed. The regions which do not coincide with the section plane to be imaged may be also scanned along a reduced number of scan lines or by a reduced number of transducers, as compared with the number of lines or number of transducers activated in the regions of the scan plane of the probe which coincide with the section plane along which imaging is to be performed.
With particular reference to three-dimensional ultrasound imaging techniques, the invention provides the combination with a three-dimensional scanning method including the following steps:
performing a three-dimensional scan of the object volume, i.e. transmitting ultrasonic signals into the object body while focusing them along individual section planes having different orientations and positions and such that all the individual section planes together cover different and predetermined sections arranged over the extension of the whole object volume, or focused on individual adjacent unit volumes which cover, as a whole, all the object body, and receiving the corresponding reflected echoes, each section plane being formed by a series of parallel and adjacent section lines, or each section slice being formed by a plurality of unit scan volumes, which are formed, in turn, by a plurality of adjacent scan lines;
and processing the received echo signals into image data in relation to their position in space with reference to scan modes;
storing image data in a memory and transforming them into image dots or lines on a video display;
the method being further characterized by the following steps:
generating a virtual volume, containing or coinciding at least partly with the volume of the object body or part thereof or a three-dimensional reference system, provided it has a precise orientation with respect to the imaging planes generated by the ultrasound probe;
setting or selecting the orientation of a predetermined section plane of the object volume or of a predetermined projection plane of said object volume prior to the scanning, processing and displaying process;
determining the lines of said selected section or projection plane which intersect the individual scan planes and/or the unit volumes coinciding with said section or scan plane.
only transmitting ultrasonic signals and receiving echoes therefrom along said lines of said selected section or projection plane which intersect the individual scan planes and/or the unit volumes coinciding with said section or scan plane.
only processing into image data and into signals for controlling the video display such reflected signals or parts thereof which are related to said lines intersecting the selected section plane or projection plane to be displayed.
In accordance with an additional improvement, the method includes the following steps:
defining a virtual volume, which at least partially coincides with or encloses the object body or part thereof or a three-dimensional reference system, with respect to a first scan plane of the ultrasound probe.
selecting and setting position and orientation parameters of the section plane or of the projection plane to be imaged, relative to said virtual volume;
identifying the transmission signals and the corresponding echoes which relate to dots, unit volumes, lines or discrete bands or slices coincident or substantially coincident with said section plane or with said projection plane to be imaged by simply comparing the position references of the dots and/or lines contained in said section plane or in said projection plane to be imaged with the scan planes of the probe;
three-dimensionally scanning the object volume only in the region coinciding with the section plane along which imaging is to be performed, and storing the received echo signals and spatial position references univocally related thereto, with reference to individual discrete dots or unit volumes and/or to discrete scanning lines or bands or slices;
relating position and orientation parameters for the section plane or projection plane which has been predetermined for imaging with the references to the spatial position of each received signal;
only processing such received echo signals which relate to dots or lines coincident or substantially coincident with the dots or lines contained in the section plane or in the projection plane to be imaged.
Advantageously, it may be arranged that the transmitted signals are only focused in certain regions or along certain lines, with reference to the lines (L1, L2, L3, Ln) or volumes of each scan plane (S1, S2, S3, Sn) and/or scan unit volume respectively, which intersect said selected section plane (P) or projection plane.
When a mixed mode in used, in which the ultrasonic signals that do not coincide with the selected section plane along which imaging is to be performed are also transmitted and received with faster and less accurate techniques, then complete processing of reflected signals is possible, simultaneously with or after processing of the signals of each line intersecting each scan plane or scan volume, i.e. even signals from regions that do not coincide with said section plane along which imaging is performed may be processed, to generate image data for the whole volume of interest, having a lower accuracy, sharpness, definition, hence a lower quality, yet being useful to complete the image near the region of interest, which coincides with the section plane along which imaging has been performed.
In order to ensure a certain reliability, scanning tolerances may be set to provide that scanning is not only performed along lines or unit volumes coinciding with the section plane along which imaging is to be performed or with the projection thereof, but also, within predetermined limits, directly adjacent to said section plane or to the projection thereof.
Three-dimensional scan modes are well-known and are addressed by several published documents, such as, for instance the ones mentioned above. Particularly, there are scan modes which perform scans of the volume along an array of successive planes having such mutual positions and orientations as to cover a succession of sections arranged over the whole extension of the object volume.
To this end, it is possible to use common linear electronic or mechanical probes, or the so-called phased array probes, or probes whose transducers are arranged on a two-dimensional surface, the so-called 2D array probes.
The displacement of probes in the third dimension, i.e. in a direction substantially transverse to scan planes or scan volumes may occur in a manual, mechanical or motorized manner, by linear indexing or by oscillation or rotation. The relative position of the individual planes is determined by comparison to a reference plane, e.g. the plane of the first scan and through position sensors which detect the position and orientation of the probe or, in the case of motorized means, through predetermined steps of the probe from its starting position.
The advantages of the present invention are self-evident in the above description. With a probe for three-dimensional imaging having substantially constant optimized scanning times, by only scanning the lines or unit volumes substantially coinciding with the section plane along which imaging is to be performed and by only processing into image data the signals pertaining to said lines or unit volumes, imaging times are drastically reduced. Moreover, by providing a complete scan with a rougher process outside the region coincident with the section plane to be imaged, a panoramic image may be obtained, which contains low-definition, low-quality information of the regions around the section plane to be imaged and high-quality information along the selected section plane. It should be also noted that the method of the invention even allows to perform complete state-of-the-art three-dimensional scans with no construction change.
Fast processing to transform the received signals into an image of the selected section plane may allow to immediately assess if the conditions in which the volume of interest has been scanned are appropriate and to possibly perform new scans with no decay of the conditions desired for imaging.
This is particularly advantageous when contrast agents are used, as it allows to perform 3D scanning or imaging operations and to assess in real time if they were performed at the right time, i.e. when the object volume was reached by contrast agents.
If this is not the case, the immediate display of the desired image plane will allow to immediately perform a second scan without the long waiting times required by prior art methods, whereby said second additional scan will be certainly performed before contrast agents decay in their effect or leave the object volume.
Times are so fast that they allow to perform a succession of several scans before decay of contrast agents or departure thereof from the object volume. This is advantageous to assess the spread of the contrast agent in the object volume in relation to time.
To this end, the method may also include parallel or separate processing of the other received signals, unrelated to the scan lines which coincide with the section plane or projection plane selected for real time display.
The invention also relates to an ultrasound imaging apparatus, particularly for three-dimensional ultrasound imaging, including:
a probe having transducers for generating ultrasonic pulses and transducers for receiving said pulses;
a unit for controlling, generating and focusing said transmitted ultrasonic pulses in accordance with predefined scan modes;
a unit for reconstructing reflected echo signals with reference to focusing modes;
a unit for converting echo signals received and reconstructed into image data and a unit for storing said image data in which said image data are related to position parameters based on scan modes;
a unit for processing said image data into signals for controlling a displaying monitor;
a unit for setting spatial orientation parameters of the section and projection planes of the object volume along which imaging is to be performed;
a unit for controlling access to image data memories and processing of said data into control signals for the displaying monitor, based on the settings of spatial orientation parameters of section or projection planes of the object volume to be imaged;
the unit for controlling the scanning process and the unit for controlling access to image data memories and processing of said data into control signals for the displaying monitor being controlled based on the settings of spatial orientation parameters of section or projection planes of the object volume to be imaged for transmission and reception, as well as for processing and storage of such signals which only relate to dots, lines or unit volumes coinciding with said selected section or projection planes along which imaging is to be performed.
Particularly, the apparatus includes a main processor whereto the means for inputting the selected orientation of the plane to be imaged and the selected ultrasound imaging modes (B-mode, Doppler, Power Doppler, Harmonic Imaging, etc.) are associated, which controls a scan control processor whereto the scanning probe is connected, a processor for converting image data into monitor control signals and a storage control processor, whereto means for storage onto physical media are connected; a RAM unit whereto the positions of the individual scanning dots, planes or unit volumes are provided by the scan processor and whereto the storage control processor and the processor for converting scans into image data, as well as the displaying monitor, are connected.
Several types of probes may be used to implement the method and in combination with the above apparatus, and particular advantages are obtained with BISCAN probes, i.e. those performing two perpendicular scans, at least one of them being motorized. These probes may be of the sectorxe2x80x94sector, linear-sector and phased array-sector type.
Nevertheless, other types of probes may be also used, such as those described in the following United States patents, each of which is hereby expressly incorporated by reference:
An accurate description of the scan modes of these probes is provided in U.S. Pat. No. 5,928,151, issued on Jul. 27, 1999 to Hossack, et al., and this description is to be intended as a part of the present description, since it embodies the state of the art and the modes for implementation of the method described above and claimed below, and is hereby expressly incorporated by reference.
Further improvements of the invention will form the subject of the subclaims.
The characteristics of the invention and the advantages derived therefrom will appear more clearly from the following description of a non limiting embodiment.
A method of ultrasound imaging according to one embodiment of the present invention comprises the steps of transmitting ultrasonic beams generated by transducers (20) into an object volume (v), receiving and storing signals generated by the ultrasonic beams in the object volume, processing the received signals into image data associated to image dots or lines of a video display, displaying at least a few image data on the display in accordance with parameters set by a user, processing of ultrasonic beams and/or displaying being specifically predetermined with reference to a preliminary selection of a section plane, characterized in that the method includes the additional steps of defining a virtual volume coincident with the object body, provided it has a definite orientation with respect to the imaging planes generated by the ultrasound probe, selecting the section plane of the object body along which ultrasound imaging is to be performed, determining the position-defining coordinates for the dots which form the section plane along which imaging is to be performed with reference to the virtual volume, restricting the scanning operation to the region which coincides with the section plane along which imaging is to be performed, transmitting the transmission signals and receiving the reflected echoes along such lines of view of the probe which coincide with the surface of the projection slice of the selected section plane, and only processing and displaying the received echo signals.
An ultrasound imaging apparatus for three-dimensional ultrasound imaging according to another embodiment of the present invention comprises a probe having transducers for generating ultrasonic pulses and receiving the ultrasonic pulses, a control unit for generating and focusing the transmitted ultrasonic pulses in accordance with predefined scan modes, a unit for reconstructing reflected echo signals with reference to focusing modes, a unit for converting echo signals received and reconstructed into image data, a unit for storing the image data in which the image data are related to position parameters based on scan modes, a unit for processing the image data into signals for controlling the displaying monitor, a unit for setting spatial orientation parameters of the section and projection planes of the object volume along which imaging is to be performed, a unit for controlling access to the image data memory and processing of the data into control signals for the displaying monitor based on the settings of spatial orientation parameters of section or projection planes of the object volume, and wherein the unit for controlling the scanning process and the unit for controlling access to the image data memory and processing of the data into control signals for the displaying monitor being controlled based on the settings of spatial orientation parameters of selection or projection planes of the object volume to the image for transmission or reception, as well as for processing and storage of such signals which only relate to dots, lines or unit volumes coinciding with the selected section or projection planes along which imaging is to be performed.
One object of the present invention is to provide and improved method of ultrasound imaging.
Another object of the present invention is to provide an improved ultrasound imaging apparatus for three-dimensional ultrasound imaging.
Related objects and advantages of the present invention will be apparent from the following description.